When a memory device using a NAND flash memory (hereinafter, referred to as a NAND memory) performs the readout of data is performed at a temperature different from temperature that is obtained at the time of the writing of data, cross temperature in which a variation in a threshold voltage is increased is generated. As a difference between temperature obtained at the time of the writing of data and temperature obtained at the time of the readout of data is increased, the change of the distribution of the threshold voltage is increased. For this reason, there is a case in which data cannot be accurately read out. As a result, the reliability of the NAND memory deteriorates. Cross temperature in the NAND memory has not been considered in the past.